Shoulder prosthesis with anatomic reattachment features

ABSTRACT

Apparatus and methods are disposed for maintaining the proper positioning of a prosthetic implant having proximal and distal ends within a prepared bone cavity during cement injection and curing. First stabilization means, implantable within the bone cavity, minimize lateral movement of the distal end of the implant, while second stabilization means, physically separate from the means for minimizing lateral movement of the distal end of the implant, minimize both the lateral movement of the proximal end of the implant and the rotational movement of the implant overall. In the preferred embodiment, the second stabilization means includes an apertured cap removably securable to the end of a bone having the prepared cavity through which the implant is inserted and held in place. This cap, which may either be entirely rigid or include a pliable membrane in the vicinity of the aperture, preferably further includes a first port associated with cement injection and a second port associated with cement over-pressurization. In an alternative embodiment, the second stabilization means includes a manually operated mechanism enabling the implant to be temporarily yet rigidly secured thereto in accordance with a desired orientation, preferably affording adjustments along multiple degrees of freedom prior to the rigid securement thereof.

REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. patent application Ser. No.10/091,846, filed Mar. 6, 2002, now U.S. Pat. No. 6,821,300 which is acontinuation of U.S. patent application Ser. No. 09/396,576, filed Sep.15, 1999, now U.S. Pat. No. 6,379,391, which is a continuation of U.S.patent application Ser. No. 09/029,457, filed Mar. 5, 1998, now U.S.Pat. No. 6,267,785, which is a U.S. national phase application of PatentCooperation Treaty application Ser. No. US97/01754, filed Jan. 31, 1997,which claims priority of U.S. patent application Ser. No. 08/595,277,filed Feb. 2, 1996, now abandoned. The entire contents of eachapplication is incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to arthroplasty and, more particularlyto devices and techniques for positioning a prosthesis prior to fixationthrough the injection of a bonding agent.

BACKGROUND OF THE INVENTION

In current joint repair situations, it is common practice to preparehost bone stock to receive an implant then, if satisfied with thephysical correspondence, apply cement to the host, install theprosthesis, and stabilize the arrangement until curing. This approachhas several disadvantages. Foremost among them arises from theunpredictable process of ensuring that, although the prosthesis may havebeen ideally placed prior to cementation, once the cement is applied,orientation may shift, resulting in a final configuration which is lessthan optimal.

A few approaches have been attempted to assist in making the positioningof the final implant more predictable. As discussed further in thedetailed description herein, one such approach utilizes a centralizingplug inserted distally within the medullary canal, and from which thereextends a rod upon which a final implant including a correspondingcentral bore may be monorailed. The plug and rod are positioned inconjunction with a trial which also includes a central bore, which isthen removed, the intramedullary cavity filled with cement and the finalimplant slid over the rod, displacing the cement as it is pushed downinto position. Although this technique may assist in maintaining aside-to-side orientation prior to cementation, it does not address thesimultaneous need for up-and-down and/or rotational stabilization.Additionally, as with current techniques, cement is applied to the hostprior to the introduction of the final implant, leaving open thepossibility that the final implant may be held in a position differentfrom that associated with the trial, and may therefore result in anunacceptable misplacement as the cement cures.

Other approaches do reverse this order, and install the final implantprior to the injection of cement. The known approaches, however, utilizea highly specialized prosthetic device including centralizingprotrusions and internal channels through which the cement isintroduced. That is, in these systems, the prosthesis itself is used asthe cement injector. Due to their requirement for a highly specializedfinal prosthetic element, such systems are incompatible with currentlyavailable implant devices, and therefore raise costs while reducing theoptions of the practitioner. In addition, they do not adequately addressthe need for simultaneously stabilizing multiple degrees of freedomprior and during cementation. As a further disadvantage, the systemswhich use the prosthesis as the cement injector tend to use the cementas a grout between the outer surface of the implant and the innersurface of the receiving cavity. It has been shown, however, that thechanges of success are improved through the creation of a thicker cement“mantle,” as opposed to a thin grout-type layer. The need remains, then,for a system whereby the prosthesis may be stabilized relative tomultiple degrees of freedom prior to cementation, and, ideally, remaincompatible with existing prosthetic components while forming a strongand stable bond to the host.

SUMMARY OF THE INVENTION

The present invention resides in apparatus and methods for maintainingthe proper positioning of a prosthetic implant having proximal anddistal ends within a prepared bone cavity during cement injection andcuring. In contrast to prior-art systems the invention provides firststabilization means, implantable within the bone cavity, for minimizinglateral movement of the distal end of the implant, and secondstabilization means, physically separate from the means for minimizinglateral movement of the distal end of the implant, for minimizing boththe lateral movement of the proximal end of the implant and therotational movement of the implant overall. In the preferred embodiment,the second stabilization means includes an apertured cap removablysecurable to the end of a bone having the prepared cavity through whichthe implant is inserted and held in place. This cap, which may either beentirely rigid or include a pliable membrane in the vicinity of theaperture, preferably further includes a first port associated withcement injection and a second port associated with cementover-pressurization. In an alternative embodiment, the secondstabilization means includes a manually operated mechanism enabling theimplant to be temporarily yet rigidly secured thereto in accordance witha desired orientation, preferably affording adjustments along multipledegrees of freedom prior to the rigid securement thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates, in skeletal form, the first step of a prior-artimplantation sequence involving host bed preparation;

FIG. 1B depicts an intermediate step in the prior-art sequence whereinthe cavity prepared according to FIG. 1A is filled with cement;

FIG. 1C illustrates the final phase of this prior-art sequence wherein afemoral prosthesis is inserted into the injected cement prior tohardening;

FIG. 2A illustrates a prior-art improvement over the sequence shown inFIGS. 1A through 1C, wherein a distal plug is used for distal centeringof the implant;

FIG. 2B illustrates yet another prior-art improvement over the approachof FIG. 2A wherein a vertically oriented rod is attached to the distalplug over which an implant may be slid after cement injection to furtherinhibit movement during curing;

FIG. 3 is an arrangement according to this invention showing the use ofa proximal cap which may be used either with a specially preparedprosthetic device or commercially available unit;

FIG. 4 illustrates two independently usable alternative embodimentsaccording to the invention, including a multiple degree-of-freedomproximal retainment structure and a distal plug including leaf springs;

FIG. 5 is a drawing which shows, from an oblique perspective, analternative embodiment of the invention which clamps around the femurbelow the area of resection, and attaches to an elongated fasteneroriented generally lengthwise with respect to the implant;

FIG. 6 is a drawing which shows how the invention could be applied to ahumeral prosthesis; and

FIG. 7 is a drawing which shows how the invention may be applied to kneearthroplasty.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 of U.S. Pat. No. 5,340,362 shows an existing, prior-art procedurefor inserting and cementing a prosthesis into a bone cavity, and thisfigure has been reproduced herein. In accordance with this technique,the canal is reamed or broached as shown in FIG. 1A, and a trial istypically inserted thereinto to ensure that the final prostheticcomponent will be properly received. After this trialing, cement isinjected into the excavated area as shown in FIG. 1B, and the prosthesisis inserted as shown in FIG. 1C, and left in position while the cementhardens. As discussed in the background of the instant invention, thetechnique just described is deficient in that, although the prosthesismay be optimally oriented during the trial procedure, the position ofthe actual implant may shift upon insertion into the cemented host orthereafter, resulting in a misaligned final fixation.

Various improvements also exist in the prior art to minimize suchadjustment problems. At the very least, as shown in FIG. 6 of U.S. Pat.No. 4,994,085, reproduced herein as FIG. 2A, a distal centralizer 16 isinserted beforehand into the intramedullary cavity 13 to which thedistal tip 17 a of the implant 17 engages at point 16 a. This, at least,stabilizes the relative position of the distal tip 17 a, resulting in anarrower range of angles (A to B) through which the implant 17 may movewithin the cement-filled cavity prior to final curing. The teachings ofthis reference further improve upon post-cementation stabilization byincorporating a stabilizing rod 4 into the distal plug 6 over which aspecially designed implant 2 having a centralized hole 4 is slidablyinstalled, as shown in FIG. 2B herein (FIG. 4 of the issued patent).Assuming the various connections between rod 5, plug 6 and the innerwalls of the intermedullary canal are relatively rigid, and the varioustolerances involved are substantially tight, movement of the implant 2is further restricted until the cement finally cures.

Another approach taken according to the prior art involves the injectionof cement after positioning of a specially designed implant into aprepared cavity. The '362 patent referenced above is directed towardsuch an approach. As with other arrangements of type, the final implantincludes a cement canal along its longitudinal axis. A bone-cementinjector is threaded onto the proximal portion of this cement canal,causing the cement to subsequently travel down and through the implant,eventually exiting through openings in and around its distal tip. Arestrictor plug halts downward cement travel, thus initiating an upward,retrograde filling of the void in between the prosthesis and thecancellous bone wall. In addition to a single distal aperture throughwhich the injected cement is introduced, side ports may also beincluded, as shown in U.S. Pat. No. 4,274,163 and various otherprior-art references.

The methods and associated apparatus just described exhibit variousshortcomings. In the technique described with reference to FIG. 2Bherein, although movements within the curing cement bed are furtherrestricted, the point of substantial stability remains at the distal tipof the implant, enabling a certain level of proximal misalignment tocontinue, as no true proximal stabilization is provided. Worse, perhaps,is that since the centering rod and bore through the specializedcomponent are both circular, the final implant is still subject toup-and-down and/or rotational variation, resulting in potentialmisalignment upon fixation.

With respect to the techniques wherein cement is injected afterinstallation, although the implant may be stabilized both proximally anddistally as the cement is injected, as with the device of the '085patent, a specially designed implant including the injector ports mustbe utilized, resulting in a specialized unit demanding significantlyhigher cost. Furthermore, regardless of the existing system utilized,attention to the pressure of the cement during injection and curing hasnot been adequately addressed. Although, for example, the systemdescribed in the '163 patent referenced above utilizes variouscomponents to maintain pressurization, numerous sophisticated articlesare required, including a high pressure nitrogen gas source, disposablecylinder and various associated valves and tubing which may be difficultto assemble, require skilled operators, or create expensive waste andmaintenance problems.

The present invention improves upon the prior art by providing asimplified apparatus and associated installation methods whereby animplant may be oriented both proximally and distally prior to theinjection of cement, while, at the same time, providing means forguarding against rotational and up/down movement of the implant as wellduring such injection and subsequent curing. In addition, configurationsaccording to the invention provide a simple means for expellingover-pressurized cement, thereby yielding a simple, but satisfactoryindication that sufficient cement has been injected to an acceptablelevel. Although, in one embodiment, the invention makes advantageous useof a longitudinal bore through the implant, in another embodiment, allof the above improvements and advantages are realized in conjunctionwith standard, currently available prostheses, thus resulting in anapproach which is both straightforward and economical.

FIG. 3 is an oblique drawing of an arrangement according to thisinvention depicting various independent embodiments. Overall, an implant310 is shown inserted into a prepared cavity 312, in this case theimplant 310 being a femoral hip prosthesis and the cavity 312 being theintramedullary canal, though, as will be apparent to those of skill inthe art of orthopedics, the general principles disclosed herein are notrestricted to this application, and may be used in other jointsituations, including the knee, shoulder and other situations. Certainfeatures of the femur are shown such as the greater trochanter 313 andlesser trochanter 315, and it is assumed that a resection not visible inthis figure has been performed on at least a portion of the proximal endof the femur along with reaming and other preparation of the medullarycanal itself to accept the implant 310.

Broadly, according to the invention, an apertured proximal sealing capis installed over the resection portion of the femoral shaft, theprosthesis 310 is inserted through the proximal opening 320 of the seal,and cement is injected through an injection port 322. In a preferredembodiment, this proximal seal includes a horseshoe-shaped collar 330having one or more means such as thumb screws 332 for releasablysecuring the collar 330 over the bone, and a preferably pliable gasket334 made from rubber or other suitable polymeric materials through whichthe aperture 320 is formed. Also located on and through this gasket 334is a flap valve 336 wherein the material forming the gasket 334 isadjusted to flap open or rupture at a predetermined pressure level,preferably on the order of 25 mm of mercury, which has shown to beadvantageous for such orthopedic purposes. Preferably, this flap valve336 is formed either by scoring the material of the gasket 334 in amanner conducive to such rupture, or, alternatively, the material may bethinned in this area to break under load.

The embodiment of the proximal seal just described is that preferred foruse in conjunction with standard, commercially available implants. Thatis, the aperture 320 formed in the gasket 334 may take the form of aslit, an oval, or another shape appropriate to the stem of the implant,enabling the device to be inserted therethrough and retained in place bythe surrounding material of the gasket 334 against the stem, eitherthrough friction or high-tolerance. Alternatively, then, if a moreprecise geometry of the stem at the point where it emerges through theproximal seal is known, the material 334 may be of a more rigidcomposition, and may, in fact, be integrally formed to the collar 330,in which case the injection port 322 and valve 336 may be more elaborateand substantial. For example, if the area 334 is metal, the port 322 maybe threaded for a more solid connection to commercially availableinjector nozzles, and the valve 336 may take advantage of moresophisticated pressure-release techniques available in the art,including adjustability for a particular pressure or range of pressures.

Whether the implant is of a standard configuration or specialized foruse in conjunction with the invention, a distal spacer 340 is preferablyutilized for distal centering. A longitudinal rod 342 may optionally beadded to, or installed on the plug 340, requiring a specialized implanthaving a longitudinal bore 344 akin to that described in the '085 patentreferred to above, the exception being that, according to thisinvention, the implant 310 would be monorailed onto the optional rod 342prior to the injection of cement into the cavity formed between thewalls of the implant and the prepared medullary canal. Thus, asdiscussed above, the present invention may either be used with aspecially prepared implant having this longitudinal bore and/orconvenient wall geometries or, alternatively, and unlike the prior art,a standard prosthesis may be used.

In the event that the prosthesis includes an arrangement to assist ininstallation or removal such as ring 350, the alternative proximalstabilization configuration of FIG. 4 may be used. To further assist inproximal securement, a multiple degree-of-freedom clamp arrangementillustrated generally at 404 may be attached to a proximal cover 406secured to femoral end or attached to a portion of available bonematerial by whatever means. In the embodiment shown, a first rod 408securely affixed to the member 406 at point 409, onto which there isdisposed a slidable collar 412 which may be locked into position with asuitable device such as thumb screw 414. A second rod 420 and collar 422contains two thumb screws, one to lock the collar 422 in position alongrod 420, and a different thumb screw 430 for positive engagement withthe prosthesis proper. It will be understood to those of skill thatvarious other approaches may be utilized in accordance with the generalprinciple contained herein to grasp and hold any portion or aperture ofa standard implant without requiring its modification.

FIG. 4 also shows an alternative distal plug according to the inventionwhich may be used in combination with any of the embodiments previouslydescribed. With such an inventive plug, it is first seated distally atan appropriate distance within the intermedullary canal, and includes aplurality of deformable upwardly oriented leaf springs 490. Accordingly,with the plug 480 installed in place as shown, an even more generalizedtype of implant, and not requiring an actual, solid connection to such adistal spacer, may be inserted down and into the medullary canal andheld in place while resisting distal side-to-side motion as the distaltip of the implant is retained within these leaf springs 490. This alsoallows adjustments in a longitudinal direction enabling fine tuning atthe effective length of the implant. Note in FIG. 4 that the aperturethrough which the implant is inserted does not include a seal per se.This is due to the fact that, in accordance with this embodiment, cementmay, in fact, be injected prior to or after the implant is held in placeboth proximally and distally. Indeed, according to this particularembodiment, a standard distal plug may be used in conjunction with themechanism shown generally at 404 even without a cap or collar as shown.For example, this mechanism 404 may simply attach to an existing bonesurface or structure instead of the point 409, thereby holding theimplant in place proximally and distally while preventing motion in alldimensions as the cement cures, regardless of when it was injected. Inaccordance with an alternative methodology, the proximal and distalstabilizers may be used in conjunction with a trial then, upon achievinga desired orientation, a single manual fastener may be loosened, and theactual implant installed in the exact configuration of the trial toguarantee proper positioning.

FIG. 5 illustrates an alternative embodiment of the invention, seengenerally at 502 from an oblique perspective. In this case, a prosthesis504, which may have a threaded bore along an axis 508 to receive athreaded fastener such as a bolt 506, is physically coupled to a firststructural element 520 which slidably engages with a collar 530, andwhich may be tightened in place with a manual fastener such as thumbscrew 532. Other types of fasteners, including those requiring toolssuch as set screws, may alternatively be utilized for this purpose. Inthis embodiment, the prosthesis 504 may be rotated about the axis 508with the bolt 506 in a slightly loosened condition, and then tightenedwhen a desired angular rotation is achieved. A score mark 522 may beused in conjunction with score marks 524 to provide an indication ofthis desired angular rotation for future reference. Preferably, scoremarks are provided on the underside of member 520 as well in thevicinity of the attachment to the prosthesis, to assist in maintainingthe desired rotational configuration once the bolt 506 is tightened.Prosthetic devices having a threaded bore along axis 508 are availablefrom the Zimmer Company, though in the event that such a feature is notprovided for, connection may be made to the prosthetic element itself asdisclosed elsewhere herein, rendering this threaded bore convenient butnot necessary to the invention.

Preferably in this embodiment a set of score marks 526 are also providedon the member 520, such that with the member 520 being moved back andforth to adjust the lateral or transverse positioning of the implant,the fastener 532 may be used to lock the configuration in place, withthe marks 526 being used to maintain a visual indication of the desiredlateral configuration. Attached to collar 530 is a downwardly extendingmember 540, which is received by a collar 544 having a manual adjustmentdevice 546. The member 540 may also include markings 542, such that, asthe element 540 is moved up and down to adjust for the axial length ofthe prosthesis, fastener 546 may be locked with the score marks 542providing a visual indication.

The collar 544 is attached to a clamp 550, which is rigidly attached tothe outer surface of the femur through manual fasteners 552 and 554. Asa further optional convenience, the collar 544 may be rotationallyvariable, and locked into place along with member 540 with manualfastener 546, with optional score marks 560 being used as a visualindication of this configuration, if so desired.

Although the various embodiments of this invention may be used toproperly position a trial implant prior to the positioning of a finalprosthetic element, it should be apparent that in all cases, the devicesuch as 504 in FIG. 5 is assumed to be the final implant itself, therebyeliminating the need for a trial. Particularly if the variouspositioning elements of the invention are sufficiently low in profile,the entire assembly, including those shown in the figures, jointreduction may be carried out, with the various fasteners beingadjustably and rigidly clamped, with the final implant positioned inplace and rigidly connected thereto. Following this procedure, theproperly positioned implant may be removed from its reducedconfiguration and cemented. According to the invention, depending uponthe circumstances, the prosthesis may be cemented in situ, with thevarious positioning members according to the invention remaining lockedin place, or, alternatively, one or more of the fasteners may beloosened, with the implant and, perhaps, other fasteners attachedthereto, removed and repositioned once cement has been injected into theintramedullary canal.

For example, referring to the embodiment of FIG. 5, fastener 546 may beslightly loosened, with the prosthesis 504 and members 520 and 540rigidly attached thereto being temporarily removed, the cavity filledwith cement, and the prosthesis with members 520 and 540 reinserted,with member 540 being reinstalled into collar 544, utilizing the scoremarks 542 to ensure that fixation will take place at a proper anddesired orientation upon re-tightening of the fastener 546. It will alsobe apparent that in the embodiment of FIG. 5 and others disclosedherein, that if the assembly attached to the femur and to the prostheticelement through using one or more structural elements according to theinvention is sufficiently rigid, positioning of the final implant may bestabilized in three dimensions (for example, rotationally, transversely,and axially—i.e., with respect to the coronal, sagittal and transverseplanes).

1. A method of positioning a shoulder implant to achieve a desiredorientation for cementation within an intramedullary canal of a humerushaving an outer cortex, the method comprising the steps of: providing ashoulder prosthesis having an articulating joint surface correspondingto a proximal humerus and an intramedullary stem; positioning theintramedullary stem within an intramedullary canal; and adjusting theorientation of the prosthesis by referring to a plurality of score markscorresponding to the orientation.
 2. The method of claim 1, wherein thescore marks indicate the rotational orientation of the prosthesis. 3.The method of claim 1, wherein the score marks indicate the depth of theprosthesis.
 4. The method of claim 1, wherein the score marks indicatethe lateral or transverse orientation of the prosthesis.